Electrolytic manufacture of caustic alkalis, &amp;c.



APPLICATION FILED MAR 12.1912.

Patented Sept. 19, 1916.

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Z4 ATTORNEYS EDGAR ARTHUR ASHCROFT, OF LONDON, ENGLAND.

ELECTROLYTIC MANUFACTURE OF CAUSTIG ALKALIS, 8w.

Specification of Letters Patent Patented Sept. 19, 1916.

Application filed March 12, 1912. Serial No. 683,378.

To all whom it may concern Be it known that I, EDGAR ARTHUR ASH- CROFT, a subject of the King of Great Britain and Ireland, and residing at 99 Buckingham Palace road, in the county of London, England, and at Sande Gaard, Balestrand, Sogn, Norway, electrochemical engineer, have invented new and useful Improvements in the Electrolytic Manufacture of Caustic Alkalis, &c., of which the following is a specification.

The object of my invention is to effect the manufacture of caustic alkalis by electrolysis in a very eflicient and economical manner so as to obtain the desired products in pure anhydrous condition and by means of apparatus which is cheap and durable.

It is well known that the methods at present employed for producing electrolytic caustic alkalis, using either mercury, or diaphragm, cells, are very costly to install, and that the process of electrolyzing chlorids in solution now universally practised is attended with considerable expense for concentrating the produced alkali solutions, and that the products cannot be obtained in a perfectly anhydrous state (suitable for instance for the indigo processes) without fur ther treatment.

Attempts to produce electrolytic caustic alkalis from fused salts have not hitherto been successful for various reasons more particularly owing to the difliculty of reacting regularly and efiiciently on sodium-lead alloys with water, or steam, and the impossibility of so reacting on potassium alloys, the vessels being very rapidly destroyed in the latter case.

My invention relates more particularly to processes in which a salt of an alkali metal (or a mixture of salts of alkali metals) is electrolyzed in a fused state in a first cell over a cathode of lead or alloy, the resulting alloy of the alkali metal and lead being then used as the source of the caustic alkali by the addition of hydroxyl. Hitherto it has been suggested to treat, in various ways, such alloys directly with water, or steam, for the desired purpose, but this method has the great disadvantage that the supply cannot be so nicely regulated that there is. never any excess of hydroxyl present, and as soon as any such excess is present the lead'is acted upon, the iron, or steel, vessels are vigorously attacked and the caustic alkali is no longer pure, or anhydrous, and, in the case of potasslum, such process becomes quite impossible. If, on the other hand, a deficient supply of hydroxyl be used, the reactions become extremely slow. These disadvantages have hitherto proved an effectual bar to the practlcal applications of such processes in spite of apparent advantages in other directions.

I have found that all difficulties are over come, and that a cheap and highly eflicient process results, if the produced alkali metal be first reacted with ammonia for the production of fused amid and the amid be then reacted with steam (preferably while the amid is still in the fused state) for the production of anhydrous caustic alkali and am monia, the hydroxyl combining with the alkali metal and the hydrogen with the radical N H of the amid.

The alloys may be produced by any known, or suitable, means, but preferably by the method and apparatus described under my application Ser. No. 683,37 5. So likewise the alkali metal, or metals, in the alloy may be reacted with ammonia by an known, or suitable, means, but preferably by the process described under my application Ser. No. 683,376.

Having produced the amid the further reaction with steam is best carried out in a separate vessel, which may however be attached to, and form part of, the complete apparatus if preferred. It will usually however be found preferable to bring the product from several, or many, electrolytic apparatuses together into one reaction apparatus. The aforesaid vessel may conveniently be a kettle of considerable capacity into which the overflow from the amid apparatus drains, and it may be provided with a slowly moving agitator for gently stirring the caustic melt. It is only necessary to introduce into the free space above this melt dry steam in small quantities, or moist air, or ammonia gas carrying moisture, to rapidly effect the conversion of the amid to caustic alkali with the production of free ammonia which is used over again. The reaction is the reverse of the reaction used in making the amid, the hydrogen lost in that reaction being supplied anew by the water.

Thus in this process (as in the well known ammonia-soda process) the ammonia acts merely as an intermediate agent and is all recovered (less trifling losses) after each cycle of operations.

. sult in producing a certain quantity of caustic alkali in admixture with the amid which becomes added to the final product. A more convenient way of working is however to pass moist ammonia first into a second, or

finishing, decomposing kettle where it simul taneously finishes the decomposition of the amid (whichhas been previously carried to near finishing point by steam in a first kettlc) and dries the ammonia for use in the amid producer. This method of procedure facilitates perfect regulation and insures great durability of the apparatus. The best temperature for these operations is from 850, to 400, centigrade, but the steaming of the fresh amid. may begin as low as 200 centigrade as mixtures of caustic alkali and amid melt at very low temperatures.

It has previously been supposed tha, alkali metal amids are dangerous substances to bring into contact with water. I have found by extensive experience that no danger arises with fused melts treated with reasonably dry steam and that the reaction proceeds quite tranquilly. The vessels in which. all the steps of this process are carried on are very durable even when .caustic potash is the product, which it is well known is a condition not possible to obtain by any other known process.

The accompanying diagram illustrates the operations.

1 represents the first cell of the electrolytic apparatus for producing the alloy, 2 represents the second cell of the electrolytic apparatus wherein the alloys are reacted upon to form amid.

3 and 4 represent the reaction kettles wherein the amid is decomposed by steam, or moist gases.

5 represents a tower which may be used for absorbing ammonia, and 6 represents an ordinary still by which the ammonia is reproduced in gaseous form.

The various connections for the gases are shown by arrows, but it will be evident that these connections may be varied in many ways. e.

What I claim is- 1. The cyclic process of producing anhydrous caustic alkalis, which consists in reacting fused alkali metal with ammonia in one cell to produce fused alkalimetal amid, running said amid into a second cell and there reacting it with steam to produce anhydrous caustic alkali and free ammonia, and returning the free ammonia to the first cell for use with a fresh quantity of fused alkali metal to produce a fresh quantity of amid for the second cell.

2. The cyclic process of producing anhydrous caustic alkalis, which consists in reacting fused alkali metal with ammonia in one cell to produce fused alkali metal amid, running said amid into a second cell and there reacting. it with steam to produce anhydrous caustic alkali and free ammonia, running the amid into a third cell, passing into said third cell the free ammonia from the second cell together with steam, whereby the conversion of the amid into anhydrous caustic alkali is completed and the ammonia dried, and returning the thus dried ammonia tothe first cell for use with a fresh quantity of fused alkali metal to produce a fresh quantity of amid for the second cell.

3. The process of producing anhydrous caustic alkali which comprises the step of subjecting an alkali metal amid to the action of steam.

4. The process of producing anhydrous caustic alkali which comprises the step of subjecting an alkali metal amid to the action of steam at a temperature above 200 C.

5. The process of producing anhydrous caustic alkali which comprises the step of subjecting an alkali metal amid to the action of steam at a temperature between 350 C. to 400 C.

6. In a process comprising the electrolytic decomposition of alkali metal salts in. a double cell apparatus, the step of introducing ammonia gas in admixture with steam into the secondary cell, the steam. being less than sufficientfor the total dec0mposition of the amid present, substantially as and for the purpose claimed.

7. The process of producing anhydrous caustic alkali which comprises the step of subjecting an alkali metal dissolved in a fused melt of amid to the action of steam at a temperature above 200 C.

8. Theprocess of producing anhydrous caustic alkali which comprises the step of subjecting an alkali metal dissolved in a melt consisting ofa mixture of alkali metal amid and alkalimetal hydrate'to the action of steam at a temperature above 200 C.

9. The process of producing anhydrous caustic alkali which comprises the step of subjecting an alkali metal dissolved in a fused melt of amid to the action of steam at a temperature of from 250400 C.

10. The process of producing anhydrous caustic alkali which comprises the step of subjecting an alkali metal dissolved in a melt consisting of a mixture of alkali metal amid and alkali metal hydrate to the action of steam at a temperature of from 350 10 400 C.

In testimony whereof I havev signed my name to this specification in the presence of two subscribing Witnesses.

EDGAR ARTHUR ASHCROFT. Witnesses:

ULYSSES J. BYWATER, PAUL ARRAS. 

